Modern disc drives are commonly used in a multitude of computer environments, ranging from super computers to notebook computers, to store large amounts of data in a form that can be made readily available to a user. Typically, a disc drive has one or more magnetic discs that are rotated by a spindle motor at a constant high speed. Each disc has a data recording surface divided into a series of generally concentric data tracks radially spaced across a band having an inner diameter and an outer diameter.
The data is stored within the data tracks on the disc surfaces in the form of magnetic flux transitions. The flux transitions are induced by an array of read/write heads. Typically, each data track is divided into a number of data sectors where data is stored in fixed size data blocks.
The read/write head includes an interactive element such as a magnetic transducer which senses the magnetic transitions on a selected data track to read the data stored on the track. Alternatively, the interactive element transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the track.
As is known in the art, each read/write head is mounted to a load arm that is supported by an actuator arm and is selectively positionable by a rotary actuator assembly over a selected data track of the disc to either read data from or write data to the selected data track. The read/write head includes a slider assembly having an air bearing surface that, in response to air currents caused by rotation of the discs, causes the read/write head to fly adjacent the disc surface with a desired gap separating the read/write head and the corresponding disc.
Typically, a plurality of open-center discs and spacer rings are alternately stacked on a spindle motor hub. The hub, defining the core of the stack, serves to align the discs and spacer rings around a common axis. Collectively the discs, spacer rings, and spindle motor hub define a disc pack assembly. The surfaces of the stacked discs are accessed by the read/write heads which are mounted on a complementary stack of actuator arms which form part of an actuator assembly. The actuator assembly generally includes head wires which conduct electrical signals from the read/write heads to the flex circuit which, in turn, conducts the electrical signals to a flex circuit connector. The flex circuit connector is mounted to a flex circuit mounting bracket, and the mounting bracket is mounted to a disc drive basedeck. External to the basedeck, the flex circuit connector is secured to a printed circuit board assembly (PCB).
The actuator assembly interacts with a magnet assembly of the disc drive to selectively move the actuator arms so as to selectively position the read/write heads. This interaction generally involves the relative movement of an electrical coil and a magnetic circuit created by a pair of opposing magnets. In one embodiment the coil is attached to the actuator assembly and rotates therewith within the magnetic field of stationary magnets. In an alternative embodiment it is known to attach the magnets to the actuator assembly and rotate them adjacent an electric coil.
In either case, the electric coil is energized with a control current to create an electromagnetic field which interacts with the magnetic circuit to move and position the actuator assembly. The recent trend in the industry is to reduce drive seek time, the time required to move the read/write head from a current data track to a target data track. One way of reducing seek time is to increase the relative amount of current to the electric coil. As the current is increased the operating temperature of the coil likewise increases, as a proportionate amount of the electrical energy is dissipated as heat energy. One skilled in the art will understand that the amount of current that can be passed through a coil is generally a function of its electrical resistance, which is directly proportional to the temperature of the coil. As the temperature of the coil increases, the magnitude of the control current is limited, adversely affecting the drive seek time. Moreover, elevated coil temperatures can also adversely affect the seek time performance by generally weakening the strength of the magnetic circuit of the magnet assembly.
There is a long-felt need in the industry for an improved actuator assembly that provides thermal heat transfer from the electric coil of the voice coil motor, so as to reduce the accumulation of heat energy in the coil to reduce the coil operating temperature.